The present invention generally relates to a sinusoidal waveform generator.
One way to obtain a sinusoidal waveform signal of a specific frequency is to directly generate the sinusoidal waveform signal. An alternative way is to obtain the same from a frequency standard through the use of frequency division techniques and other conventional techniques.
In the former method, sinusoidal waveform signals of accurate frequency are obtainable by utilization of crystal resonators, mechanical resonators, etc. However, in particular ranges of frequency, no proper elements such as crystal resonators are found.
In the latter case where the desired sinusoidal waveform signal is to be obtained from the frequency standard through the use of the frequency division technique, the sinusoidal waveform signal in any range of frequency may be obtained easily with the aid of recent developments in digital integrated circuits. Because the waveform is rectangular, it is difficult to alleviate any harmonic wave distortion through a simple filter. Therefore, when it is desired to utilize the thus obtained signal as the sinusoidal waveform signal, a variety of difficulties are encountered.
Accordingly, it is an object of the present invention to provide a sinusoidal waveform signal generator which is able to provide sinusoidal waveform signals in any desired range of frequency with a substantial reduction in the harmonic wave distortion therein.
In order to achieve the above described object, pursuant to the concept of the present invention, a rectangular waveform signal is first provided at a frequency four times higher than the frequency of a desired sinusoidal waveform signal to be generated, and thereafter frequency-divided by two and four through the use of a couple of binary counters. Subsequent to this, a predetermined step waveform signal is provided via two resistors and an adder in accordance with the states of the respective counters. The harmonic wave components thereof are removed via a filter.